Greenhouse gases emitted by human activity are strengthening storms and causing rain bands and dry zones to move poleward, scientists report November 11 in the Proceedings of the National Academy of Sciences.

Climate simulations have long forecast that climate change caused by greenhouse gas emissions will make rain heavier and more intense, while also pushing storms and deserts away from the equator. Observed climate patterns that match these predictions are called "fingerprints" of human activity. Researchers have struggled to find such fingerprints because weather is notoriously fickle.

In the new study, Kate Marvel and Céline Bonfils, climate scientists at Lawrence Livermore National Laboratory in California, develop a statistical method to separate human influence from natural variation in precipitation. The researchers use the method to see whether satellite and ground-based rain measurements from 1979 to 2012 matched predicted fingerprints. Marvel and Bonfils find that storms had indeed strengthened, and both storms and deserts had migrated toward the poles.

Only human influence can account for these trends happening in tandem, Marvel and Bonfils conclude.